1. Field of the Invention
This invention relates generally to methods of and apparatus for orienting devices, and, more particularly, to methods of and apparatus for orienting asymmetrical semiconductor devices by use of a helical magnetic chute.
2. Description of the Prior Art
In the semiconductor industry, many devices, such as diodes, are often electrically asymmetrical. These devices have a different set of electrical characteristics depending on their orientation; when they are oriented in a first direction, they have one polarity and when oriented in a second direction they have an opposite polarity.
Although this electrical asymmetry may also be accompanied by a physical asymmetry of the outer body of a device, it does not necessarily have to be. Thus, it may be impossible to tell the polarity of the device simply by looking at its outer body.
One way to overcome this difficulty is to electrically test the devices and separate them according to their polarities. U.S. Pat. No. 3,731,783 to D. H. Dreher et al. is an example of such a system. This patent is assigned to the assignee of record and is herein incorporated by reference. Once the devices have been separated, it is desirable to orient them all into a common polarity to allow them to be recombined for coding and packaging operations. Generally, the coding operation includes marking an indication of polarity on the devices' outer body.
In recombining the separated devices, a number of techniques have been developed. For example, in systems having separate bins for each polarity, one bin may be turned around so that the devices therein then have the same polarity as the other bin. This, however, requires removal of one of the bins which is time-consuming and cumbersome. Furthermore, since an operator generally does the turning around of the bin, human error may result from a lack of attentiveness.
In other prior art techniques, diodes are automatically oriented after separation. This is accomplished by placing a spirally slotted cylinder in the path of one group of the diodes. The body of each diode stays within the cylinder while the leads extend outwardly through the slots. As the diodes fall through the cylinder, the spiral slot turns the leads so that the devices rotate 180.degree. to the desired polarity. One serious drawback of this system, however, is that the slot must be relatively narrow since the devices could slide out if it were large enough for the bodies of the devices to pass through. Because of the narrowness, the slot will quickly clog up from any dirt buildup from the device. Also, any device misalignment or bends in the leads may cause jamming. Another problem is that no force other than gravity exists to urge the devices into the turning cylinder or to keep them in alignment to avoid clogging.